10. Adsorption Behavior of Ruthenium on Chitosan

Kiyoko Imai, Yoshikazu Nishimura and Kazuo Watari

Keywords: ruthenium, adsorption behavior, chitosan, sodium chloride solution

The chemical characteristics of ruthenium are quite complicated, because ruthenium possess many oxidation states and related compounds. Therefore, radioruthenium produced in relatively high fission yield shows complex behavior in nuclear fuel reprocessing, radioactive waste treatment, environmental samples and in the human body.

In this study the authors have made experiments on the adsorption behavior of ruthenium on ehitosan which is the deacetylated derivative of chitin. Chitin is distributed widely in nature, especially in shellfish and insects. This material is a cellulose-like biopolymer and known to be a natural chelating agents with adsorption ability for some heavy metal ions. This adsorbability is mainly due to the amino group presence.

Adsorption experiments were carried out by the batch method to investigate the effect of chemical forms of ruthenium on the adsorption. Ten ml of sample solution containing 10-200g of ruthenium labelled with ¹⁰³Ru and 0.1g of chitosan were stirred in an erlenmeyer flask. Adsorption percentage was obtained by measuring the radioactivities of ¹⁰³Ru in the supernatant solutions before and after a 20-hour agttatuon.

First, adsorption of chloro complexes of ruthenium (¹⁰³Ru(III,IV)) on chitosan was examined in distilled water, 1M hydrochloric acid solution and 1M sodium chloride solution. Ruthenium was effectively adsorbed in distilled water and 1M sodium chloride solution, while adsorption was negligible in 1M hydrochloric acid solution. Adsorption behavtor of chloro complexes and high oxidation state ruthenium anions (¹⁰³Ru(VI)O₄^2-, ¹⁰³Ru(VII)0₄^-) on chitosan and cellulose powder is shown in Table 3. Chitosan had relatively high adsorbability for both ruthenuum SPCICI(IIS, whule adsorptuon on cellulose was greatly influenced by its chemical forms.

For comparison, other important radionuclides such as the fission products, ¹³⁷Cs, ⁹⁰Sr and ¹⁴⁰Ba or induced radioactive products,⁶⁰Co, ⁵⁹Fe and ⁶⁵Zn were also examined using sodium chloride solution. It was found that chitosan could adsorb ⁶⁰Co ⁵⁹Fe and ⁶⁵Zn. However, these nuclides except ⁵⁹Fe were hardly adsorbed on cellulose. Adsorption of ¹³⁷Cs, ⁸⁵Sr (to simulate ⁹⁰Sr) and ¹³³Ba (to simulate ¹⁴⁰Ba) was negligible on both adsorbents.

The results showed that adsorption of radionuclides such as ⁶⁰Co, ⁵⁹Fe and ⁶⁵Zn on chitosan was due to the formation of chelate compound. In the case of ruthenium, we thought that adsorption of chloro cornplexes was mainly due to formation of chelate compound, while adsorption of high oxidation state anions was due to formation of insoluble ruthenium dioxide (RuO₂) by reduction.

In radiochemical analysis, an adsorption method is often used as the first step for concentrating and separating of desired radionuclides. Chitosan was successively applied to separating radionuclides of alkali and alkali earth elements from radioruthenium and other nuclides of transition elements.

Table 3. Effect of Chemical Forms on Adsorption of Ruthenium from 1M Sodium Chloride Solution

[Ru:200g/10ml]

�@ Ru-chloro(III,IV) RuO42-RuO4- cellulose powder 5(%) 75% chitosan 80(%) 95%